The invention relates to a motor vehicle having an axle support arranged between a drive unit and a vehicle occupant compartment.
An axle support, frequently also called a subframe or an auxiliary frame, is a component of many passenger cars having a self-supporting vehicle body. The vehicle-body-side linkage points of the wheel suspensions are fastened to the axle support. Also fastened to the front end subframe are usually the engine, the transmission, the steering gear and, in the case of vehicles with driven front wheels, the differential. The axle support may be rigidly screwed (integral support) to the vehicle body or may be connected to the body by way of rubber bearings. In the case of modern motor vehicles, the axle support frequently has the basic shape of an internally open rectangle or trapezoid.
From European Patent document EP 1 036 689 A2, an axle support of a passenger car is known which, viewed in the direction of travel, is arranged slightly behind a drive unit. The lower ends of two struts are linked to the axle support at its region situated in the front in the direction of travel, which struts are mounted with their upper end regions on engine side members of the body of the passenger car. By way of two rearward-extending supports, the region of the axle support that is in the rear in the direction of travel is connected with supporting vehicle body components in the forward lower region of the vehicle occupant compartment of the vehicle body. The linkages of the struts to the engine side members and to the linkages of the supports to the supporting vehicle body components in the forward lower region of the vehicle occupant compartment can, in each case, be abruptly released by an explosive charge when a frontal impact of the motor vehicle is detected. As a result, the displacement path of the drive unit becomes free toward the rear in the direction of travel. The entire space between the vehicle occupant compartment and the drive unit can be utilized for a displacement. The elements that deform in the event of an accident, such as the engine side members, can thus deform unhindered by the axle support, whereby a large amount of impact energy can be absorbed.
It is an object of the invention to further develop the known motor vehicle having an axle support.
This and other objects are achieved by a motor vehicle according to the invention, having a front end which is arranged in front of a vehicle occupant compartment. A drive unit, for example, an internal-combustion engine, is arranged in the front end. An axle support, on which the vehicle-body-side linkage points of the wheel suspensions of the front wheels are mounted, is situated between the drive unit and the vehicle occupant compartment. The rearward region of the axle support is connected by way of at least one rearward-extending support with a supporting vehicle body part in the forward lower region of the vehicle occupant compartment of the vehicle body. For this purpose, the support is connected with the supporting vehicle body component by a pyrotechnically releasable connecting element. In addition, a guide is arranged between the rearward end region of the support and the vehicle body element, which guide exclusively permits a rearward displacement of the guided end region of the support, as viewed in the direction of travel, if the connection is released by the pyrotechnical connecting element between the support and the vehicle body element. Such a pyrotechnically releasable connecting element may, for example, be a pyrotechnical separating screw, a pyrotechnical separating bolt or a pyrotechnical detent. For the purpose of this invention, all pyrotechnical connecting elements have in common that they contain a pyrotechnical explosive charge. When this pyrotechnical explosive charge is ignited, the connecting element will be damaged so severely or even be destroyed that the connection previously established by it is released. In the case of the use according to the invention, the pyrotechnically releasable connecting element can form a form-locking connection between the support and the vehicle body element, as long as it was not triggered. After the triggering, the pyrotechnical connecting element is destroyed to such an extent that this form-locking will no longer exist or will only exist to such a reduced degree that even low forces will be sufficient for completely releasing the connection.
Such a pyrotechnical separating screw is known, for example, from German Patent document DE 195 32 746 A1. Such a separating screw makes it possible to ensure a stable screwed connection which can be abruptly released by the triggering of a pyrotechnical separating charge. In the event of a detected collision of the vehicle, the pyrotechnical separating screw is preferably triggered with a considerable frontal component, so that this connection is released. For this purpose, the separating screw may be coupled with an air bag control device, so that the separating screw is triggered, for example, simultaneously with the driver's or front passenger's airbag.
Advantageously, the pyrotechnical connecting element can be electrically triggered, the electric line being guided to the pyrotechnically triggerable connecting element from the interior of the vehicle occupant compartment. As a result of the guiding of the electric line through the interior, the line is situated in dry space and is protected from external damage.
In the event of a detected collision, the pyrotechnically releasable connecting element is preferably triggered with a considerable frontal component, so that the connection between the support and the vehicle body element formed by the pyrotechnical connecting element before the triggering will be released.
The arrangement according to the invention permits a robust, simply designable linkage of the axle support to the body of the motor vehicle. When a crash of the motor vehicle with a considerable frontal component is detected, the pyrotechnical connecting element connection, by which the at least one support is linked to the vehicle body component, is abruptly separated, for example, by the air bag control device. As a result, the support is now only connected with the vehicle body component by way of the guide. When the drive unit is now displaced in the rearward direction as a result of the crash, the drive unit strikes against the axle support, so that, viewed in the direction of travel, very high forces act upon the axle support and thereby also on the linkage of the at least one support at the vehicle body component. The support thereby shifts toward the rear. This displacement takes place in a controlled manner, guided by the guide. Defined by the guide, the axle support can thereby escape toward the rear, so that more space is available in the front end, in order to absorb crash energy by targeted deformation. Nevertheless, the axle support is not completely separated from the motor vehicle, so that thereby no additional danger will arise.
The rearward end region of the support and the vehicle body element advantageously mutually overlap in the direction of travel, whereby the rearward end region of the support rests against the underside of the vehicle body element. In a particularly advantageous further development, the guide between the rearward end region of the support and the vehicle body element can be formed by an oblong hole in the support or in the vehicle body component extending in the direction of travel. A guiding element projects through the oblong hole at the—viewed in the direction of travel—rearward end, which guide element is connected with the vehicle body component or with the support. Care should be taken in this case that, also in the event of high acting forces, the guiding element will always project through the oblong hole, so that guidance is ensured. The length of the oblong hole thereby limits the maximal displacement path of the rearward end region of the support and, thereby, of the axle support relative to the vehicle body element toward the rear. The guiding element may, for example, be formed by a screw, which is screwed into the vehicle body component or into the support, and thereby presses the support onto the vehicle body component. As a result, the head of the screw rests against the lateral regions adjoining the oblong hole. The forces acting upon the guide in the case of a crash are so high that the holding force is overcome by which the screw presses the support onto the vehicle body component. After the overcoming of the holding force, the screw only still causes a frictional force between the support and the vehicle body element which, however, is clearly lower than the holding force. In addition, the frictional force contributes to the desired energy absorption. Should this frictional force not be desired, so that, in the event of a crash, the axle support can shift to the rear in a manner that is even more unhindered, the thickness of the component with the oblong hole, in the region of the oblong hole, can decrease in the longitudinal direction of the oblong hole toward the front, viewed in the direction of travel. As a result, the screw will lose its tension force already after a slight displacement in the oblong hole, so that it can also no longer generate any frictional force.
Preferably, the—viewed in the direction of travel—forward region of the axle support is connected by way of struts with the engine side members extending above the axle support, which—viewed on the direction of travel—extend from a front wall of the vehicle passenger compartment toward the front and are used, among other things, for accommodating a front bumper. These struts increase the stiffness of the linkage of the axle support to the rest of the vehicle body. In the event of a crash, they do not represent any significant resistance when the axle support is displaced toward the rear. They buckle primarily in the region of their linkage points to the engine side members and/or to the axle support.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.